This invention relates to a check valve and, more particularly, to a removable check valve especially suited for installation in a submersible pump.
Submersible pumps are often employed in wells, such as water wells, in which they are positioned several hundreds of feet below ground. In such an installation, the submersible pump is suspended by a long drop pipe or delivery pipe which is connected to the discharge head of the submersible pump. Thus, when the pump stops, the delivery pipe is full of water, so that water under considerable pressure will flow back through the pump, spinning the pump and the motor in reverse. Such reverse spinning is undesirable and can be harmful to the submersible pump and its motor. In addition, when the water flows back out of the delivery pipe, the pipe fills with air which must be moved out before water flows at the outlet on the ground surface.
In view of these problems, it has been common practice to place a check valve at the bottom of the delivery pipe to prevent the backflow of the water or other fluid being pumped. As a convenience, a check valve is now often built into the submersible pump, usually in the outlet in the discharge head, so that a check valve need not be installed separately.
It is desirable for a number of reasons that check valves built into submersible pumps be removable. For example, dirt or sand from the well often becomes lodged in the check valve, interfering with the smooth operation of the check valve and causing it to stick. Thus, it is desirable for the check valve to be removable for cleaning. Furthermore, some pump servicing operations can be performed if there is access to the inside of the pump through the outlet. Servicing in this manner eliminates the need to remove the discharge head or otherwise disassemble the pump, and providing a removable check valve permits the necessary access.
In some submersible pump applications, such as in shallow well installations, the height of fluid in the delivery pipe is not enough to cause damage by spinning the pump and motor backwards. Thus, a check valve is not needed in such an application and a removable check valve can easily be taken out, if desired.
Also in some pump systems, such as in domestic water systems, a storage tank at the ground surface is used to provide a limited amount of water for use in the system, so that the pump need not work each time water is drawn from the system. In such a storage tank, compressed air is commonly employed to force the water out of the tank and into the system. If the check valve is omitted from the submersible pump in such a system, the water will drain from the delivery pipe and the delivery pipe will fill with air when the pump stops. The air in the delivery pipe will then be compressed by the pumped water when the pump starts. This compressed air can be directed to the storage tank to provide the means for forcing the water out of the tank and into the domestic water system. Thus, in such a system, it is desirable that the check valve be removable to allow the water to drain from the delivery pipe, yet it is important where the delivery pipe is long that the water not be permitted to rush back through the pipe and spin the pump and motor in reverse.
In some submersible pump applications, the pump supplies liquid to piping systems which are buried in the ground but, because of rock strata or other considerations, cannot be buried deep enough to prevent the water inside from freezing. As in the case of water systems having storage tanks employing compressed air, it is desirable to let the water drain out of the delivery pipe, so that the water in the piping which is subject to freezing will drain, but it is again important not to allow the water flow with enough force to damage the pump or motor by reverse spinning.
Where known check valves have been employed in pumps installed in systems in which the backflow of water out of the delivery pipe has been desired, it has been a practice to drill a hole through the check valve to allow the water to drain. Of course, this renders the valve inoperable for later regular use.